The present invention concerns a system for verifying the presence and identity of a tube connector connected to an instrument and, more particularly, an electro-optical method and device to determine whether a tube assembly has been connected to a fluid analyzing instrument and, if so, whether it belongs to a certain class of such tube assemblies.
The particular application for which the present invention will be described is that of a capnograph, which is an instrument for analyzing exhaled air. A capnograph is used by sampling air exhaled by a patient, by means of a small tube, also called sampling line, one end of which is, for example, connected to an air passageway of a respirator or to a cannula attached to the patient""s nostrils; the tube is connected at its other end, through a special connector, to the analyzing instrument. The tube assembly, especially of the type that is the subject of the present invention, often includes a filter or other means for removing moisture and mucus; alternatively, there may be a filter built into the capnograph or supplied separately, to be connected to the tube. The complete tube assembly, including the filter and the connector, is usually of the disposable type and is replaced for every patient tested.
A typical connector, also referred to as a luer, is depicted in FIG. 1, which shows the two members, one male and one female, separated; each member is shown in an isometric view and in a longitudinal section. The shape of the connector, which is essentially round, as depicted in Fig. l, is standardized throughout the industry, so that tube assemblies of various manufacturers may be interchangeably used with any analyzing instrument. Thus, the manufacturer of a particular type of analyzing instrument has generally no control over which type of tube and filter will be used with his instrument in practice. For reasons of optimal functioning of the instrument, as well as for commercial reasons, the manufacturer of an analyzing instrument may want to exert such control. In particular, he may want to stipulate that only a certain class of tube assemblies be connected to, and used with, his instrument. Such a class may, for example, consist of tube assemblies that include a filter, in general, or such that are manufactured directly by him or to his specifications or under his supervision or license. in particular.
One way to enforce this stipulation would be to use some unique interlocking key arrangement between the connector and the instrument. Such an arrangement would, however, be incompatible with the standard connector shape being used throughout and would require of the operator, when connecting and disconnecting the tube, different motions than those to which he is used.
Another way of enforcing the stipulation is to have a system by which the correct tube assembly would be identified as such by the instrument, whereupon its operation would be enabled, and to disable the instrument otherwise. A side benefit of such an arrangement would be that the instrument would be prevented from operation also when no tube is connected at all or when even a correct tube is improperly connected, thus avoiding damage to sensitive parts of the instrument and also causing incorrect readings. Yet another purpose may be served by such a system, namely identifying the tube assembly as belonging to one of a number of classes and informing the instrument of the particular identity detected, so as to enable it to automatically operate differently for the different classes.
There are known several types of means for effecting such identification. One type is electro-mechanical, whereby the connector would have one or more protrusions or notches at its end. which would engage appropriately placed levers that activate micro-switches. This type of means is impractical, because of the small dimensions of the connector pair and the little space available at the surrounding instrument panel. Another type of means is electrical, whereby the connector would have one or more conductive paths at its end, which would complete the circuit between appropriately placed contacts. This type of means is impractical, because of the dampness prevalent in the immediate surroundings.
There is thus a widely recognized need for, and it would be highly advantageous to have, a fluid analysis system that includes the capability of determining that a tube assembly has been properly connected to the analyzing instrument and that the tube is of a certain class. Such a capability must be compatible with the standard shape of connectors being used, as well as with the medical environment, must be reliable and must preferably be inexpensivexe2x80x94at least with regard to the fabrication of the disposable tube assembly.
The present invention successfully addresses the aforementioned needs by providing an air analysis system in which the presence and classification of a connected tube assembly can be conveniently and reliably detected.
The present invention discloses a novel modification of an air analysis system, whereby the presence of a tube connector of an acceptable class and its proper placement with respect to a mating connector, is ascertained by making the end of the connector appropriately reflective and by shining light thereon and detecting the light reflected thereof.
More specifically, the system of the present invention provides for a specularly reflective surface on the end of the tube connector of the acceptable class and for a pair of optical fibers mounted in the mating connector so that when, and only when, that tube connector is correctly positioned, a sufficient portion of light emitted from the end of one fiber is reflected into the end of the other fiber. The emitted light originates from a pulsed LED, optically coupled to the first fiber. The light reflected into the other fiber is detected by means of a photo-diode connected to a circuit that includes a comparator. The latter outputs a binary signal that can be used to enable or disable essential components of the analyzing instrument.
In an alternative configuration, the end of the tube connector has a fluorescent or phosphorescent material, which can be stimulated by the light emitted from the first fiber to re-emit light of spectral chareteristics different from those of the LED. A portion of the re-emitted light is collected by the second fiber and is passed through a spectrally selective filter, then detected as in the first configuration.
According to the present invention there is provided an apparatus for analyzing fluid supplied to it through a tube and a system for verifying the proper connection of the tube thereto and for classifying the tube, comprising:
an analyzing instrument within an enclosure;.
a first connector attached to the tube and having an end face;
a second connector, mating with the first connector and attached to the enclosure;
a pair of optical fibers disposed inside the enclosure, a first end of each of the fibers being mounted in the second connector so that, when the first connector is properly mated with the second connector, there is a clear optical path between the end face of each of the first ends of the fibers and at least one common point on the end face;
a light source optically coupled to the second end of a first fiber; and
a light detector optically coupled to the second end of the second fiber.
According to further features in preferred embodiments of the invention described below, the end face is essentially specularly reflective over at least an annular portion thereof, the analyzing instrument is operative only upon reception of an enabling signal and further comprises an electric circuit connected to the light detector, the circuit being configured so that only if a substantial portion of any light emitted from the first end of one of the fibers is reflected by the annular portion of the end face into the first end of the other one of the fibers, will the circuit output the enabling signal to the analyzing instrument.
Preferably, the light source emits light in a narrow band of wavelengths and the apparatus further includes an optical filter, essentially transmissive of the narrow band of wavelengths and disposed in the path of the light transmitted through the second fiber. According to a modification of the preferred embodiment, the reflectivity of the end face is spectrally selective and the light source emits light in a narrow band of wavelengths, or there is a spectrally selective optical filter disposed in the path of the light transmitted through the second fiber.
According to another configuration, the end face is coated with a fluorescent or phosphorescent material, the light source emits light in a first band of wavelengths, such that stimulate the fluorescent or phosphorescent material to emit light in a second band of wavelengths, and the apparatus further includes an optical filter, essentially transmissive of at least one wavelength of the second band and disposed in the path of the light transmitted through the second fiber. According to a modification of this configuration, the second band of wavelengths is different among a plurality of types of the material and the optical filter of a particular apparatus is transmissive of the band corresponding to only one type.
According to further features in the described second configuration, the light source emits light as a first train of pulses and the circuit further includes a synchronous detector that is fed with a multiplying signal formed as a second train of pulses, the two trains of pulses having equal rates and the second train being delayed with respect to the first train.
There is also disclosed herein a method for verifying the proper connection of a tube to a fluid analyzing instrument and for classifying the connected tube, utilizing a system essentially as disclosed herein.